Glow-discharge vessel filled with gas or vapor



J. NIIENHOLD Aug. 13, 1935.

GLOW DISCHARGE VESSEL FILLED WITH GAS OR VAPOR Filed Dec. 16, 1952 Aa/elven;

Patented Aug. 13, 1935 UNITED STATES GLOW-DISCHARGE VESSEL FILLED WITHGAS on VAPOR Johannes Nienhold, Berlin-Charlottenburg, Germany, assignorto Siemens & Hals'ke, Airtiengesellschaft, Siemensstadt, near Berlin,Ger.. many, a corporation of Germany Application December 16, 1932,Serial No. 647,554

In Germany December 18, 1931 12 Claims.

This invention refers to an improvement of gasor vapor-filledglow-discharge vessels, having a hollow cathode. Where in the followingdescription and in the appended-claims reference is made to aglow-discharge hollow cathode, this. is understood to be a cathodesubdivided so as to form spaces or compartments, the different componentparts of such cathode being arranged in such a manner and at such adistance apart that the electrons liberated from one portion of thecathode by the impingement ofpositive ions are shot into the cathodicfall space of the opposite part of said cathode and are stopped in thisfall space, thus giving rise to a concentration of electrons in thehollow spaces of the cathode and, consequently, to a reduction of thecathode fall.

A glow-discharge hollow cathode is more particularly understood to bealso such a one of the type characterized above, in which the distancesseparating the opposite hollow cathode surfaces are equal or inferior tothe fall space thickness at a simple cathode.

In the accompanying drawing, Fig. 1 is a diagram illustrating thedischarge conditions; Figs. 2, 3, 5, 6, '7 and 8 are vertical sectionsillustrating various embodiments of my invention; and Fig. 4 is aperspective view of 'a perforated hollow cylinder such as I employ insome of the embodiments shown.

' In glow-discharge vessels having such glowdischarge hollow cathodes,the operating conditions employed prior to my invention are such as arerepresented, for instance for small gas pressures in Fig. 1.

The discharge current i has been plotted as abscissa and the filamentvoltage e as ordinate. On applying a voltage to the vessel the voltagemust, for instance, be raised to 300 volts (section a-b). At thisvoltage, a low discharge, known vto-day usually as preliminarydischarge, is started, while the voltage simultaneously decreases to 200volts (section b-c). For further increase of the filament voltage thedischarge current increase is comparatively slight, so as to give asteep rise of the characteristic line (section cd) At 900 volts, point11, the preliminary discharge suddenly becomes the glow-dischargestrictly speaking, the voltage dropping from 900 volts to about volts(section d-e) The voltage of 180 volts depends, of course, on the seriesresistance. The discharge current intensity decreases considerably withincreasing filament voltage (section e-f). At point the glow-dischargeis converted into the are disways.

charge (section ;f g), which involves a voltage drop of from say 400volts to 15-20 volts. The range g-h is the arc discharge range. As maybe seen from the characteristic line, a very high voltage should beapplied at least once, in orderto obtain appreciable discharge currents,i. e. at least one glow-discharge. In the case of the example, it wasnecessary to raisethe voltage once up to 900 volts for a mean operatingvoltage and for a glow discharge of 200-400 volts.

The smaller the gas pressure, the higher the maximum voltage tobeapplied before the starting of the glow-discharge The same holdsforsmall cathode distances. The dotted curve c-k indicates, for instance,such a characteristic for l charge hollow cathode, as defined above,suitable means for obtaining a supplementary thermal production ofelectrons in the hollow spaces. For this purpose devices well-known inthemselves are available. The method of making hollow cathodes highlyemissive by the use of adequate material is well-known in the art. Theinner surfaces of hollow cathodes are, for instance, coated with alkaliearth metals or oxides of electro-positive' substances or finelysub-divided compounds of the two. priate design of the cathode, withrespect to the working current, permits one also to obtain a certainself-heating efiect, which is, however, only obtained after at least therange of high glow-discharge currents has been reached. Thus these meansdo not result in a considerable reduction of the voltage peak (point din Fig. 1;). Only an additional source of thermions, as employed in thisinvention, enables a direct passage tobe obtained from point 0 to pointe sothat th peak is avoided (hatched range).

The thermionic source can be designed in two Either use is made of anincandescent cathode, of a type known in the art, for instance, anoxide-coated, distillation or thoriated cathode, orprovision is made foradditional heating enabling the hollow cathode or at least parts of itto emit ions thermically.

The first case in which use is made of a directacting incandescentcathode has been represented An approby the electrode holding wire 2 orits extensionin Fig. 2. The holding wire 2 sealed into the squash lcarries the glow-discharge hollow cathode 3 which has been given theshape of a box. It consists of a casing 4 surrounded by a heatprotectingenvelope 5. Within the cathode there are located the intermediate sheetsorpartitions 6, '1 and 8, which are bored through in the middle, so asto enable the helical filament [0 carried 9 to project into the wholeof-the compartments formed by the said partitions, which compartments inthis particular example are designated by l I; I2, l3 and M. Thehelical'filament is atone end supported by the holdingwire I'5,whichis"insulated by means of an insulating tube. ILB .andled throughthe casing 4 and the heat-protecting envelope 5. Of course the filamentcani'be given. any other form. The lead to the filament, which may alsobe a stretched filament, may be insulated at both ends, afact which isof importance for A. C.

" operation. It is -also' possibleto establish an electric connection'between the electric center of the "filament and thelhollow cathodesystem.

' 'Another example of the use of a directly heated cathode is given by'Figs. 3 and 4. The two elec- '-trode holding wires l'a' are sealed intothe squash l'l. Theycarry the hollow cathode'which is, in

"this case, builtupo'f concentrical cylindersZl and 22 arrangedinthe-casing T9 surrounded by the heat-protecting envelope-.20. Thesecylinders. are shapedas indicated in Fig. 4, i. e. they. have slotsenabling the various compartments of the cathode 'system to communicatewith one another. Within thehollow cylinder, 2l, there is located a"double-wound helical "filament 23 carried by the -two electrode holding:wiresflkand 25. The slots'of the different 'hollow cylinders aredesigned-so as i to enable the electrons emitted within the hollow 1cylinder 2 I =to i penetrate into the other compart- 'ments. The'bariumvaporrcloud formed 1 byithe thermite pill 26 (compound:of barium-oxideand aluminium) can also during the manufacturing process penetrate-through i the-slotsinto all the compartments.

When starting a'hot cathodersuch as'indicated in Figs. 3 and 4,it'isifound that the glow-discharge "within cylinder irisfirststartedand that dueto I the superposed dischargecurrent; thehot cathode a isthen brought to a brighterglow (additional "hollow cathode 29 which, .asshowniin ,the concaused to emit electrons.

I self-heating). The dischargeshifts to the re- -=maining hollowcylinders,"the-hot (cathode again assuming its normal temperature.

When the glow-discharge'is started, it is, with suitable design of thecathode, possibletto switch the hot-catho'de-o'fi" or to keep it burningat a "dark-red glow. V r 1 Figs. 5-8 show thehollow cathodes,-asheated-ine directly according to" the invention.

In Fig. '5, the electrodeiholding wire i28 sealed into the squash 21carries 'the "glow-discharge structional example of Figs. 24,- consistsofiiacas- *ing or cylinder39 whichmay be surmund'ed'by a-heat-protectingenvelope '3 I. Wi'thin30, there is, for mstance,= aho'llow cylinderfj32, and, in its center a convex bulge-53 containingwithin its inner concave part a "heater 34 "heated, for instance,

"through :the lead 36 surrounded by-tan insulating -tube 35. Afterswitching on the .heater, .34, the' 'part 33 is heated up,'sothatitszouter surface is In the case of C. heating, lt mayfbeelectricallyrecommendable to .separate the heating wire 34 completely:fromthe hollow cathode system. .In the casepf the above-':described:glowedischarge .hollowacathodez also.,%the

- same :manner as :in the previous ,-example. ..heater:52whichiisplacedwithinthe met/a1 19012259 7 inner cylinder 32 or thepartitions should be equipped with openings, so as to enable theelectrons proceeding from the outer surface of the cylinder 32, topenetrate into all the compart-- ments under consideration. 7 I W Fig.,6 shows another constructional example of the glow-dischargehollow'cathode. The squash 31 carries the holding wire 38 for the hollowcathf ode 39. "4.8cloSeda-atthertop and containing a heater it! "heatedin a manner well-known in the art. The tube 40 carries spaced circularribs 42 so that 41 :between theribs 42 with an electron emittingmaterial, e. g. oxide .or the like, in order to obtain,withinthe'liniits' possible, a high electronic outalso heated and it maythen be desirable to coat these ribsas well with an electron-activematerial This hollow cathode consists of a tube.

' compartments-"43,"!4545 etc. are formed. It may Y gbeisuitable in this.case to coat the tube parts t6,

-put. FIf the heating is suflicient, the ribs are. 1 c c or to'construct them ithroughout o'f such material i for example thoriatedtungsten or the= like).

Figsfl'l and 8 show dischargeives'sels :according to my invention,- -inwhich the heating "is indi rect, the heater, "however, being locate'd'outside H the discharge vessel, that is notwithin the vacuv um. In thisway-"the heaters can be-readily interch'anged and the discharge vesselscanxmore particularly "be adapted for any given working conditions bythe insertion of 'anadequate'heat'er body. I J

3mg; shows-a vessel in which theI heaten-is located within .a smallxbayzof itheqdischarge :vessel. Themetalpot 50 is =sealedat-49 &into the:discharge vessel 48vconsisting :for :iinstancel of glass and carryingthe glow-vdischarge ihollowrcathede This cathode is constructed inmuch-rt-he {The as arin-g. isyplaced-aroundithe=metalrpoti-from theoutside, andrraises the temperatureqof the cath- .ode .to a degreessuitable for emission-purposes,

'A tapered cross-section maybezprovidediforwat "26! in order to blockthe transmissionzof heat.

On account-ref the -g-reatstraln produced by the :heating,thej'metalnpotsfill. 0fIF ig.1' 7 and-510i :8 shouldbe madezof metal-:not :readilyroxidized, for instance ."Of .chromic 'iron, xnickel-iironor the alike, or :they should he coated with: nickel-.,-:chr.o-

'miumtor platinum-l-ayem'on, he side-'exposed 'to ithe ratmosphere.

Asitothematei'ial forithe cathnde, Ifmayuse tnickel, iron,molybdenumxungsten, .:or the ilike, either in the compactcondition-or in'thesshape 60f *a netting. nsshaseibeen stated above, theemis- :sivematerial should i'be either thorium in: any of its 7 difierent formsorealkali earth metalslas well *as the oxides 'theredf. -?Moreparticularly in the constructional examples shown in :Figs. 7 8,

-mate'ria'ls should he :used .which event at ex 1 treme'ly-lowtemperatures 'willyield a "high emis--- sion of-electrons..Bariumf'finel-y sub-:divided-with oxide; 'which 'evenf.:at temperaturesbelow ;red-

glow will yield an appreciable emission, is of special suitability. Theuse of nettings (nickel) is here'preferable, as it suits theemission-material particularly well. From the manufacturing standpointnettings are also recommendable, since, for instance, barium-oxide caneasily be rubbed into the meshes, and pure barium is present in thenettings after disintegration in vacuo.

As to the construction of the hollow cathode. the following isimportant: the distances separating the opposing hollow cathode surfacesshould be in a definite ratio to the filling gas and to the gaspressure, i. e., the distances should be inferior or equal to the widthor thickness which the fall space has in the case of a cold simplecathode under corresponding conditions as to kind and pressure of thegas or vapor employed. By a simple cathode, I mean one made of sheetmetal, a so-called plate cathode, opposite to which an anode is locatedat a relatively considerable distance. This distance varies with thekind of gas or vapor employed and with the pressure under which such gasor vapor is contained in the vessel. These distances, insofar as theycannot be determined by experiment, can be calculated roughly, by makingthem equal to 10 to 20 times the length of the mean free gas-kineticelectron path.

The electron path length within a gas or vapor having a pressure of 19mm. is:

, perature of C., are as follows:

I-Ig Ar Ne Iie By multiplying these values by -20 we approximatelyobtain the fall space thickness at a gas pressure of 1 mm.

A distinguishing feature of my invention is the production of a peculiareffect known as the hollow cathode effect. Investigations have shownthat this effect is obtained when using a subdi vided cathode havingcompartments the adjacent walls of which are spaced from each other adistance smaller than twice the thickness of the fall space. Anexplanation of this peculiar effect is found in various publications,see for instance Engel & Steenbecks book Elektrische GasentladungenBerlin 1934, Section 49 (pages 114 to 116).

What I claim as my invention is:

1. In a glow-discharge vessel filled with gas or vapor and having aglow-discharge hollow cathode, provided with compartments, the distancebetween the adjacent walls of such compartments being smaller than twicethe thickness of the fall space, means for the additional thermicproduction of electrons within the compartments of the cathode.

2. In a glow-discharge vessel filled with gas or vapor and having aglow-discharge hollow cathode, provided with compartments, the distancebetween the adjacent walls of such cornpartments being smaller thantwice the thickness of the fall space, a hot cathode located withinvapor, a glow-discharge hollow cathode provided with compartments, thedistance between the adjacent walls of such compartments being smallerthan twice the thickness of the fall space, said cathode containing anelectric heater.

4. In a glow-discharge vessel filled with gas or vapor and having aglow-discharge hollow cathode, provided with compartments, the distancebetween the adjacent walls of such compartments being smaller than twicethe thickness of the fall space, a heater located outside the dischargevessel.

5. In a glow-discharge vessel filled with gas or vapor and having aglow-discharge hollow cathode, provided with compartments, the distancebetween the adjacent walls of such compartments being smaller than twicethe thickness of the i all space, a heater located outside the dischargevessel and surrounding said glow-discharge hollow cathode.

6. In a glow-discharge vessel filled with gas or vapor and having aglow-discharge hollow cathode, provided with compartments, the distancebetween the adjacent walls of such compartments being smaller than twicethe thickness of the fall space, a heater located outside the dischargevessel within a bay of the walls.

7. In a glow-discharge vessel filled with gas or vapor and having aglow-discharge hollow cathode, provided with compartments, the distancebetween the adjacent walls of such compartments being smaller than twicethe thickness of the fall space, a heater located outside the dischargevessel and within a bay having the shape of a sealed-in pot.

8. In a glow-discharge vessel filled with gas or vapor and having aglow-discharge hollow cathode a heater, provided with compartments, thedistance between the adjacent walls of such compartments being smallerthan twice the thickness of the fall space, located outside thedischarge vessel in a bay having a tapered cross-section.

9. In a glow-discharge vessel filled with gas or vapor and having aglow-discharge hollow cathode provided with compartments, the distancebetween the adjacent walls of such compartments being smaller than twicethe thickness of the fall space, and means for the additional thermicproduction of electrons in the compartments of said cathode, openingsconnecting said hollow spaces with one another and enabling thethermically produced electrons to penetrate into several compartments.

10. Glow-discharge vessel filled with gas or vapor and having aglow-discharge hollow cathode provided with compartments, the distancebetween the adjacent walls of such compartments being smaller than twicethe thickness of the fall space, and means for the additional thermicproduction of electrons within said compartments, means for insulatingsaid hollow cathode from heat.

11. A device of the character described, comprising a glow-dischargevessel filled with gas or vapor and having a glow-discharge hollowcathode provided with compartments and in which the opposing surfaces ofthe different component parts are at distances from each other inferioror equal to the thickness which the fall space has in the case of asimple cathode under corresponding conditions as to kind and pressure ofthe gas or vapor employed, and means for the additional thermicproduction of electrons within: said cathode.

12. A deviceof the characterdes'cribed, comprising aglow-dischargeevessel filled with gas or 5 vapor and having. aglow-discharge hollow cathode. having opposing surfaces the distanceWhichthefaILspaceLtmsJ-in the case ofa simple cathode undercorresponding conditions as to kind and pressure of the gas or vaporemployed, and means for the additional thermic production ofelectrons-within'said cathode.

JOHANNES NIENHOLD.

